As more and more electronic devices are made with digital controls; and as the devices become smaller and smaller, the need for low to medium force actuators that can operate on low power has steadily increased. There are very few basic mechanisms that are impulse driven and can efficiently translate an electrical pulse into linear mechanical motion. A requirement that the motion be silent makes the design even more difficult, and will eliminate most of the electromechanical devices now being used.
The most common electrical device for deriving linear motion is the solenoid coil, with a moving core plug. It is, however, very inefficient because of large air gaps involved; and it makes a great deal of noise when the iron plug hits bottom. The movement of the center core is very quick, with very little stall force; consequently, it cannot store or integrate its force over a period of time, to transfer the energy relatively slowly into a high inertia load.
There are rotary solenoids which translate a short center core motion, thru balls in a sloped race, into a rotational motion, of the order of 20 to 30 degrees. This type does have the ability to store more energy during the rotation; however, it is still very quick; and it is reciprocal. It must return by spring loading to its original position, which robs it of useable power during the power stroke. This type of solenoid is also very noisy.
It is, therefore, one object of this invention to provide an efficient Rotary D.C. motor like device, which, with an added brush contact to the armature, and suitable drive circuitry, can be used as a relatively silent single turn rotary actuator; which, with the use of a suitable cam or bell crank, can produce a single linear motion with each single electrical impulse.
Most magnetically actuated devices at present, such as the solenoid and the relay type mechanisms, have power curves that are inversely proportional (by square law) to the size of the magnetic air gap. Consequently, the start-up or "stall" power drops off quickly as the required distance of movement increases. Since most impulse devices would work best with maximum applied power up front, or stored for concentrated use relatively late in the drive cycle, the conventional air gap devices are quite out of phase with the requirements.
It is, therefore, another object of the invention to utilize the efficient design of a conventional D.C. motor which (1) has a very small air gap between the armature poles and the field magnets, (2) Has an efficient and relatively slow build up of inertia in the armature as the armature speed builds up and, (3) The energy that is stored in the weight and speed of the armature can be used in a short burst at a later part of the rotational cycle; with greater peak power available at the end of the cycle. Through the use of cams or bell cranks; and without the need of reciprocating back to the start position with spring loading, there is more energy available during the "work" cycle.
In miniature equipment in the medical field, and in particular, the controllers that are used with I.V. infusion sets, the need for dependable silent operation is very important. When the control device is driven in periodic impulses from digital controls, it is usually to save average power, so that small batteries can be used for back-up during power emergencies; or for completely portable operation.
It is, therefore, still another important object of this invention to provide an efficient and relatively silent single turn actuator, which is completely magnetically accelerated and stopped, without mechanical impacts. The life expectancy of the all magnetic actuator, based on even a toy D.C. motor, is at least 10,000 hours; since the impulse operation at typically once per second will be several hundred times the 50 hour life rating at 15,000 revolutions per minute.
A further feature of the invention is the very low cost to produce; since the basic small D/C. motor components are presently being made to very high precision,and in extremely large production quantities.